Process for the preparation of triethylenediamine (TEDA)

ABSTRACT

A process for the preparation of triethylenediamine (TEDA) by reaction of ethylenediamine (EDA) in the presence of a zeolite catalyst, wherein  
     the zeolite catalyst comprises one or more metals M in oxidation states II, III or IV as oxides, and  
     for M=Al, has an SiO 2 /M 2 O 3  molar ratio of greater than 1400:1,  
     for M=metal in oxidation state II or M=two or more metals in oxidation state II, has an SiO 2 /MO molar ratio of greater than 100:1,  
     for M=metal in oxidation state III or M=two or more metals in oxidation state III, has an SiO 2 /M 2 O 3  molar ratio of greater than 100:1 and  
     for M=metal in oxidation state IV or M=two or more metals in oxidation state IV, has an SiO 2 /MO 2  molar ratio of greater than 10:1,  
     and the reaction temperature is from 250 to 500° C.

[0001] The present invention relates to a process for the preparation oftriethylenediamine (TEDA) by reaction of ethylenediamine (EDA) in thepresence of a zeolite catalyst.

[0002] Triethylenediamine (TEDA=DABCO®=1,4-diazabicyclo[2.2.2]octane) isan important basic chemical and is used, inter alia, in the preparationof pharmaceuticals and plastics, in particular as catalyst in thepreparation of polyurethanes.

[0003] The known processes for the preparation of TEDA essentiallydiffer through the nature of the starting materials and the catalysts.It is basically advantageous for the starting materials employed to befavorable basic chemicals, for example monoethanolamine (MEOA) orethylenediamine (1,2-diaminoethane, EDA). However, conventionalprocesses have proven to have very low selectivity, in particular withrespect to the starting material EDA. In addition, the removal of theimpurities which form during the cyclization reaction is difficult, andconsequently these processes have not been able to establish themselvesin industry.

[0004] The process described in U.S. Pat. No. 3,285,920 (H. G. Muhlbaueret al., Jefferson Chemical Co.) for the simultaneous preparation of TEDAand piperazine (referred to as PIP below) is a two-step process in whichfirstly EDA, ethanolamine and/or oligomers thereof are reacted in thepresence of ammonia and hydrogen to give a mixture of piperazine andN-(beta-aminoethyl)piperazine in a reductive amination process usingmetal-oxide hydrogenation catalysts, and the remainder after removal ofthe piperazine is cyclized in the presence of cyclization catalysts,such as phosphate salts and aluminosilicates. The yields of TEDA areabout 25% and those of PIP are about 12%.

[0005] U.S. Pat. No. 2,937,176 (Houdry Process Corp.) relates to thepreparation of TEDA by gas-phase reaction of an alkylenepolyamine oralkanolamine in the presence of a solid acidic catalyst, such assilica-alumina, at temperatures of from 300 to 500° C. The TEDA ispurified by crystallization from hydrocarbons, preferably pentane.

[0006] DE-A-24 34 913 (Shunan Petrochemicals) (equivalent: U.S. Pat. No.3,956,329) describes the use of pentasil zeolites for the synthesis ofTEDA from amines, such as N-aminoethylpiperazine, PIP or EDA, byreaction on zeolites of types A, X and Y of the general formulaa(M_(2/n)O) (Al₂O₃) m(SiO₂), where M=an alkali metal, alkaline-earthmetal, an element from the zinc group, H⁺ or NH₄ ⁺; n=valency of thecation; a=1.0+0.5; n=2−12. For conversion into the desired form, thezeolites are treated with an aqueous solution of hydrochloric acid forion exchange with hydrogen cations or with metal halides for ionexchange with the desired metal cations.

[0007] EP-A-158 319 (Union Carbide Corp.) relates to the preparation of1-azabicyclo[2.2.2]octane and 1,4-diazabicyclo[2.2.2]octanes fromacyclic or heterocyclic amines in the presence of a ‘high-silicazeolite’ catalyst.

[0008] EP-A-313 753 (equivalent: DE-A1-37 35 212) and EP-A-312 734(equivalent: DE-A1-37 35 214) (both Hüls AG) disclose a process for thepreparation of a PIP/TEDA mixture by reaction of ethanolamines and/orethylenediamine in the presence of a zeolite of the pentasil type. Inaccordance with the process, the reaction mixture is passed in gaseousform over a fixed-bed catalyst at from 280 to 380° C., and LHSV (liquidhourly space velocity) of from 0.1 to 10 h⁻¹ and at an absolute pressureof from 0.1 to 10 bar. It is also proposed that the starting compoundsbe employed together with a diluent, for example water. Maximum TEDAselectivities of 46% are achieved.

[0009] According to EP-A-382 055 (equivalent: DE-A-39 03 622, BASF AG),1,2-diaminoethane (EDA) and from 0 to 200 mol % of piperazine areconverted into TEDA on aluminum, boron, gallium and/or iron silicatezeolites under the following preferred reaction conditions, in the caseof a liquid-phase reaction: reaction temperature from 100 to 300° C.,pressure from 1 to 5 bar and WHSV from 1 to 10 h⁻¹. The reaction ispreferably carried out in the gas phase at a reaction temperature offrom 200 to 400° C., a pressure of from 0.5 to 5 bar and an WHSV of from1 to 10 h⁻¹. A solvent or diluent, such as water, may be added. In thepreferred gas-phase procedure, yields of TEDA of up to 70% are obtained.As a particular preparation procedures, treatment with aqueoushydrochloric acid after the shaping of the zeolites, and subsequentcalcination at from 400 to 500° C. is described.

[0010] EP-A-423 526 (equivalent: DE-A-39 34 459, Bayer AG) describes aprocess for the preparation of TEDA and PIP by reaction of EDA onzeolites of the pentasil type with reduced acidity. According to thethis application, zeolites of this type are obtainable by exchange of atleast 50% of all exchangeable cations by alkali metal cations or arethose in which the aluminum of the zeolite structure is replacedisomorphically by iron. According to this application, ZSM-5 catalystswhich have not been treated by this process have proven to be lesssuitable. The reaction is carried out at a temperature of from 300 to400° C. and at a weight hourly space velocity of from 0.03 to 2.0 kg(EDA)/kg (zeolite)/h, using EDA/water mixtures comprising from 2 to 25mol, preferably from 5 to 15 mol, of water per mole of EDA.Selectivities with respect to TEDA of up to 65% are achieved.

[0011] U.S. Pat. No. 4,966,969 (Idemitsu Kosan) describes a method forthe preparation of TEDA from amine-containing compounds, for examplemonoethanolamine, ethylenediamine, piperazine or piperazine derivatives,on metal silicates of the pentasil type which have SiO₂/Al₂O₃ ratios ofgreater than 12 and which have been calcined at 400-600° C. under air,at reaction temperatures of 100-500° C. and pressures from 3 bar.

[0012] U.S. Pat. No. 5,041,548 (Idemitsu Kosan Ltd) proposes, interalia, using pentasil zeolites (SiO₂/M₂O₃: for example H-ZSM5,SiO₂/Al₂O₃=45-90) prepared in the presence of organic templates, such astetraalkylammonium compounds, in the reaction of amine-containingcompounds, for example monoethanolamine, ethylenediamine or piperazine,for the preparation of TEDA. In the reaction of EDA/water mixtures at400° C., TEDA yields of 45% are achieved. Pentasil zeolites preparedwithout an organic template exhibit significantly worse TEDA yields inthe reactions of the amine-containing compounds at 350-400° C.

[0013] EP-A-831 096, EP-A-842 936 and EP-A-952 152 (Air Products andChemicals Inc.) describe processes for the preparation of TEDA from EDAor monoethanolamine using specially modified pentasil zeolites:

[0014] According to EP-A-831 096 (equivalent: U.S. Pat. No. 5,731,449),caustic lye treatment of a pentasil zeolite (Na-ZSM5, SiO₂/Al₂O₃=160)which has subsequently been converted into the H⁺ form by means ofNH₄NO₃ solution and calcination (H-ZSM5, SiO₂/Al₂O₃=153) enables anincrease in the selectivity with respect to TEDA from 23% to 56% and inthe long-term stability to 32 hours to be achieved without visibledeactivation in the reaction of an EDA/water mixture at 340° C. comparedwith untreated zeolites. The effect is explained by passivation of theactive centers (hydroxyl groups, analysis by IR spectroscopy) on theexternal, outer surface of the zeolite as a consequence of thecaustic-lye treatments.

[0015] According to EP-A-842 936 (equivalent: U.S. Pat. No. 5,741,906),pretreatment with a dealuminating agent (chelating agent for removal ofaluminum, for example oxalic acid) likewise enables the external, outersurface of pentasil zeolites (H-ZSM5, SiO₂/Al₂O₃=180) to be passivatedand thus, for example, improved selectivity to be achieved in thesynthesis of TEDA from monoethanolamine, piperazine and water at 350° C.of up to 30% compared with untreated zeolites.

[0016] According to EP-A-952 152 (equivalent: U.S. Pat. No. 6,084,096),surface passivation of the pentasil zeolites can likewise be achieved bytreatment with a silicon compound followed by calcination. The treatmentof a very finely crystalline pentasil zeolite (H-ZSM5, SiO₂/Al₂O₃=90,crystal size: 0.07 μm) with a solution of tetraethoxysilane in ethanolfollowed by calcination enabled, for example, the selectivity withrespect to TEDA and PIP in the reaction of an EDA/water mixture at 340°C. to be increased from 81% to 89% compared with the untreated materialwith a slight drop in activity.

[0017] EP-A-842 935 (equivalent: U.S. Pat. No. 5,756,741) (Air Productsand Chemicals Inc.) describes a two-step process in which firstly apiperazine-rich intermediate is prepared from an amino compound by acyclization reaction, and this intermediate is then converted into TEDAwith addition of, for example, EDA on a pentasil zeolite. It is claimedthat this special two-step procedure minimizes or even eliminates thenecessity for PIP recycling in the synthesis of TEDA.

[0018] EP-A-1 041 073 (Tosoh Corp.) relates to a process for thepreparation of triethylenediamines and piperazines by bringing certaincompounds containing an aminoethyl group into contact with a crystallinealuminosilicate in which the silica/alumina ratio is at least 12. Theshaped aluminosilicate is calcined at a temperature of 500-950° C.,preferably at 550-850° C., for at least one (preferably 3) hours. Thecalcination is followed by acid treatment with an aqueous inorganic acidat 50-80° C. for from 3 to 50 hours.

[0019] U.S. Pat. No. 4,289,881 (Bayer AG; equivalent: EP-A-10 671)describes the preparation of TEDA from certain piperazine derivatives inthe presence of an SiO₂ catalyst.

[0020] DD-A-206 896 (VEB Leuna-Werke) relates to a process for thepreparation of TEDA by reaction of N-(beta-aminoethyl)piperazine and/orN-(beta-hydroxyethyl)piperazine on a porous SiO₂/Al₂O₃ catalyst in thepresence of NH₃.

[0021] Derwent Abstract No. 1997-371381 (RU-A-20 71 475 (AS SibeCatalysis Inst.)) describes the preparation of triethylenediamines frommonoethanolamine on a pentasil zeolite which has been treated with anaqueous solution of a complexing agent.

[0022] RU-C1-21 14 849 (Institute for Technology and Construction ofCatalysis and Adsorption Processes using “Tseosite” Zeolite SO RAN)(Derwent Abstract No. 2000-036595) describes processes for thepreparation of TEDA from a mixture of monoethanolamine (MEOA), EDA andPIP on pentasil zeolites having a modulus (SiO₂/Al₂O₃ molar ratio) of40-300. The zeolites used are dealuminated by treatment with an aluminumchelating agent (EDTA, sulfosalicylic acid, TMAOH). The patentspecifically describes the reaction of MEOA/EDA, MEOA/PIP, EDA/PIP andEDA/MEOA/PIP mixtures with NH₃ or water as diluent (1:3-10) oncorrespondingly treated zeolites at 350-450° C. The reactor product isseparated into boiling ranges by rectification. The range 160-180° C. issubsequently cooled and crystallized out. The mother liquor isre-employed as starting material.

[0023] A common feature of the prior-art processes is the lowselectivity with respect to the formation of TEDA, a very high and thuspossibly uneconomical proportion of water as diluent or solvent in thereactor feed, an inadequate catalyst service life, for example as aconsequence of deactivation, and possibly in addition complex catalystpreparation and/or modification.

[0024] It is an object of the present invention to find an economicalprocess for the preparation of TEDA from readily accessible startingcompounds which is improved compared with the prior art, is simple tocarry out, has high yield, selectivity and catalyst service life and lowunavoidable formation of piperazine and which gives the TEDA in highpurity, color stability (i.e. low color number in accordance with ISO6271, which also remains small over extended storage times, for example6, 12 or more months, and odor quality [i.e. is possible only as aninherent odor of TEDA and no odor of cyclic saturated N-heterocycliccompounds with 5-membered rings or other cyclic saturated N-heterocycliccompounds with 6-membered rings (for example PIP or N-ethylpiperazine)and/or aromatic N-heterocyclic compounds with 5- or 6-membered rings].

[0025] We have found that this object is achieved by a process for thepreparation of triethylenediamine (TEDA) by reaction of ethylenediamine(EDA) in the presence of a zeolite catalyst, wherein

[0026] the zeolite catalyst comprises one or more metals M in oxidationstate II, III or IV as oxides, and

[0027] for M=Al, has an SiO₂/M₂O₃ molar ratio of greater than 1400:1,

[0028] for M=metal in oxidation state II or M=two or more metals inoxidation state II, has an SiO₂/MO molar ratio of greater than 100:1,

[0029] for M=metal in oxidation state III or M=two or more metals inoxidation state III, has an SiO₂/M₂O₃ molar ratio of greater than 100:1,and

[0030] for M=metal in oxidation state IV or M=two or more metals inoxidation state IV, has an SiO₂/MO₂ molar ratio of greater than 10: 1,

[0031] and the reaction temperature is from 250 to 500° C.

[0032] The process according to the invention can be carried outbatchwise or preferably continuously.

[0033] The reaction according to the invention can be carried out in theliquid phase or preferably in the gas phase.

[0034] The reaction is preferably carried out in the presence of asolvent or diluent.

[0035] Examples of suitable solvents or diluents are acyclic or cyclicethers having 2 to 12 carbon atoms, such as dimethyl ether, diethylether, di-n-propyl ether or isomers thereof, MTBE, THF, pyran, orlactones, such as gamma-butyrolactone, polyethers, such as monoglyme,diglyme, etc., aromatic or aliphatic hydrocarbons, such as benzene,toluene, xylene, pentane, cyclopentane, hexane and petroleum ether, ormixtures thereof and particularly also N-methylpyrrolidone (NMP) orwater or aqueous organic solvents or diluents of the abovementionedtype. Ammonia is also a suitable solvent or diluent.

[0036] The particularly preferred solvent or diluent, in particularlysolvent, is water.

[0037] Suitable diluents when carrying out the reaction in the gas phaseare also inert gases, such as nitrogen (for example beyond thesaturation of the reactor feed) or argon. The reaction in the gas phaseis preferably carried out in the presence of ammonia.

[0038] For example, the reaction is carried out in the presence of from2 to 1200% by weight, particularly from 12 to 1200% by weight, inparticular from 14 to 300% by weight, very particularly from 23 to 300%by weight, of solvents or diluents, based on EDA employed.

[0039] For example, the starting mixture employed in the process or thereactor feed (=starting material stream in the case of the continuousprocedure) comprises from 5 to 80% by weight, particularly from 10 to80% by weight, particularly preferably from 20 to 70% by weight, veryparticularly preferably from 20 to 65% by weight, of EDA and from 2 to60% by weight, particularly from 10 to 60% by weight, particularlypreferably from 15 to 60% by weight, in particular from 20 to 50% byweight, of the solvent(s) and diluent(s).

[0040] In a particular embodiment of the process according to theinvention, EDA and one or more amine compounds each containing a2-aminoethyl group, —HN—CH₂—CH₂—, are reacted.

[0041] Amine compounds of this type are preferably ethanolamines (forexample monoethanolamine (MEOA), diethanolamine (DEOA) ortriethanolamine (TEOA)), piperazine (PIP), diethylenetriamine (DETA),triethylenetetramine (TETA), tri(2-aminoethyl)amine,N-(2-aminoethyl)ethanolamine (AEEA) and piperazine derivatives, forexample N-(2-hydroxyethyl)piperazine (HEP) andN-(2-aminoethyl)piperazine (AEPIP).

[0042] PIP is particularly preferred.

[0043] The content of these amine compounds in the reactor feed is inthis particular embodiment (in total) generally from 1 to 1000% byweight, preferably from 3 to 250% by weight, in particular from 7 to250% by weight, in each case based on EDA employed.

[0044] For example, the starting mixture employed in the process or thereactor feed (=starting-material stream in the case of the continuousprocedure) comprises (in total) from 0.5 to 50% by weight, preferablyfrom 2 to 50% by weight, in particular from 5 to 50% by weight, of theseamine compounds.

[0045] Since it has also been found that in this particular embodimentthe formation of by products which can only be removed from the reactorproduct (=product stream in the case of the continuous procedure) withdifficulty can occur in the starting mixture or in the reactor feed ifMEOA is employed, the content of this amine compound in the startingmixture or reactor feed is preferably from 1 to 50% by weight, based onEDA employed.

[0046] After the reaction, the products formed are isolated from thereaction product mixture by conventional methods, for example bydistillation and/or rectification; unreacted starting materials can befed back into the reaction.

[0047] Thus, PIP arising in the reaction product mixture from theprocess according to the invention can be removed therefrom, for exampleby distillation, and fed back into the reaction.

[0048] A particular advantage of the process is that intermediatefractions containing both TEDA and piperazine which are obtained onwork-up of the reaction product mixture, and fractions which contain,for example, N-(2-hydroxyethyl)piperazine (HEP),N-(2-aminoethyl)piperazine (AEPIP), diethylenetriamine (DETA),triethylenetetramine (TETA), tri(2-aminoethyl)amine and/orN-(2-aminoethyl)ethanolamine (AEEA) can be fed back into the reactionagain.

[0049] Furthermore, unavoidable formation of other amine compounds fromother amine cyclization/condensation reactions can be fed to thereaction according to the invention without the yields of TEDA beingsignificantly impaired.

[0050] In a particularly preferred embodiment, the process according tothe invention is carried out, in particular in the case of thecontinuous procedure (steady state), by reacting EDA and from 14 to 300%by weight of water and from 7 to 250% by weight of PIP, in each casebased on EDA,

[0051] preferably EDA and from 23 to 300% by water and from 8 to 250% byweight of PIP, in each case based on EDA,

[0052] particularly preferably EDA and from 33 to 250% by weight ofwater and from 17 to 250% by weight of PIP, in each case based on EDA,

[0053] very particularly preferably EDA and from 110 to 185% by weightof water and from 25 to 100% by weight of PIP, in each case based onEDA.

[0054] In this embodiment, the proportion of the PIP or EDA can also bereduced or increased to the extent of from 0.01 to 20% by weight, forexample from 0.01 to 10% by weight, in favor of one and at the expenseof the other.

[0055] For example, the starting mixture employed in the process or thereactor feed comprises in this particularly preferred embodiment from 10to 60% by weight of water, from 20 to 70% by weight of EDA and from 5 to50% by weight of PIP,

[0056] preferably from 15 to 60% by weight of water, from 20 to 65% byweight of EDA and from 5 to 50% by weight of PIP,

[0057] particularly preferably from 20 to 50% by weight of water, from20 to 60% by weight of EDA and from 10 to 50% by weight of PIP,

[0058] very particularly preferably from 45 to 55% by weight of water,from 30 to 40% by weight of EDA and from 10 to 30% by weight of PIP,

[0059] where the proportion of the PIP or EDA can also be reduced orincreased to the extent as described above in favor of one and at theexpense of the other.

[0060] In this particularly preferred embodiment of the process, thereactor feed, in addition to EDA, PIP and water in the above-statedmixing ratios or amounts, preferably comprises less than 10% by weight,particularly less than 5% by weight, in particular less than 2% byweight, of further components.

[0061] In this particularly preferred embodiment, it has been found thatat the above-stated mixing ratios or amounts of the starting materials,the reaction, in particular in the case of the continuous procedure (inthe steady state) can be carried out in such a way that EDA is convertedvirtually completely (i.e. conversion greater than 95%, in particulargreater than 97%) into TEDA and PIP with a selectivity of greater than90%, in particular greater than 95%.

[0062] The process is preferably carried out in accordance with theinvention by setting an appropriate EDA/PIP ratio in the reactor feed(=starting-material stream in the case of the continuous procedure) inthe abovementioned ranges so that the consumption of PIP in the overallbalance approaches zero (for example from 0 to 30 kg, in particular from0 to 15 kg, very particularly from 0 to 10 kg, per 100 kg of TEDA in thereaction product mixture), in particular is zero, through removal of PIPfrom the reaction product mixture and recycling into the reactor feed,and at the same time the EDA employed is reacted completely (>95%, inparticular >97%, very particularly >99%), i.e. as a result essentiallyno additional PIP is fed to the process according to the inventionduring the continuous procedure.

[0063] Since, if the reaction is carried out in this way, the amount ofdischarged EDA approaches zero in accordance with the invention, theseparation of the reactor product mixture, for example by distillationand/or rectification, is particularly simple in this process variant.

[0064] The reaction temperature in the process according to theinvention is preferably from 300 to 400° C., particularly preferablyfrom 310 to 390° C.

[0065] The starting-material components or the reactor feed areadvantageously brought to temperature in advance.

[0066] For carrying out the process according to the invention, thefollowing reaction conditions have furthermore proven favorable:

[0067] a WHSV (weight hourly space velocity), based on the aminesemployed in the reaction, of from 0.05 to 6 h⁻¹, preferably from 0.1 to1 h⁻¹, particularly preferably from 0.3 to 1 h⁻¹, and

[0068] a pressure (absolute) of from 0.01 to 40 bar, particularly from0.1 to 10 bar, preferably from 0.8 to 2 bar.

[0069] Suitable reactors in which the process according to the inventionis carried out are stirred-tank reactors, in particular tubular reactorsand tube-bundle reactors.

[0070] The zeolite catalyst is preferably arranged in the reactor in theform of a fixed bed.

[0071] The reaction in the liquid phase can be carried out, for example,by the suspension, trickle or pool method.

[0072] The preferred reaction in the gas phase can be carried out in afluidized bed or preferably fixed bed of catalyst.

[0073] The following paragraph additionally outlines by way of examplehow the process according to the invention can be carried out:

[0074] The reactor feed (composition as described above) is convertedinto the gas phase in an evaporator, which may, if desired, be part ofthe actual reactor, at a temperature of 250-500° C. and fed onto thecatalyst. The reaction product mixture arising in gas form at thereactor outlet is quenched at temperatures of 20-100° C., preferably at80° C., by liquefied reaction product mixture circulated by pumping.This liquefied reaction product mixture is worked up as follows: in afirst distillation step, low-boiling components, such as acetaldehyde,ethylamine, ammonia and water, and heterocyclic compounds formed asby-products in the synthesis are separated off. In a second distillationstep, the reaction product mixture is freed from piperazine, which isfed back to the reactor feed. The stream of separated-off piperazinehere may comprise up to 20% by weight of TEDA. (Alternatively, it isalso possible to remove water and piperazine simultaneously, which canbe fed back together into the reactor feed). In a preferred distillationstep, the target product TEDA is recovered from the reaction productmixture by distillation and, if necessary, worked up further, forexample in a subsequent crystallization step (for example as describedbelow).

[0075] The following advantages, inter alia, are achieved with theprocess according to the invention:

[0076] The process allows the EDA employed as starting material to bereplaced, depending on price and availability, by one or more aminecompounds each having a 2-aminoethyl group, —HN—CH₂—CH₂—, (see above),or these amine compounds additionally to be added to the reactor feed.

[0077] Piperazine, essentially the only by-product, can, if the reactionis carried out in a suitable manner as described above, be fed back intothe process and converted into TEDA. Mixtures of unreacted piperazineand TEDA can also be fed back to the catalyst, since it has been foundthat TEDA is stable under the reaction conditions.

[0078] Given a suitable choice of the EDA/PIP ratio in the reactor feedas described above, the consumption of PIP in the overall balanceapproaches zero, since on recycling of the PIP present in the reactionproduct mixture, a constant PIP stream in terms of volume is obtained inthe reactor feed and thus exclusively EDA as the only amine in theoverall balance must be fed continuously to the reaction from theoutside.

[0079] High selectivity and high conversion, based on the reaction ofEDA to give TEDA, are achieved.

[0080] Owing to the zeolite catalysts used in accordance with theinvention, fewer by-products are formed in the reaction of EDA and, ifused, the abovementioned amine compounds, which results in simplifiedwork-up of the TEDA formed in the process in order to achieve therequisite product specifications (purity, color number and odor).

[0081] The zeolite employed as catalyst in the process according to theinvention for the preparation of TEDA has a skeletal structure whichprincipally consists of silicon dioxide (SiO₂).

[0082] Besides silicon dioxide, the zeolite may also contain traces ofother divalent, trivalent or tetravalent metals M (oxidation state ofthe metals II, III or IV) in the form of metal oxides M_(2/z)O (z=2, 3or 4), where the molar ratio of silicon dioxide and the metal oxide,SiO₂/M_(2/z)O (this molar ratio is also known as the ‘modulus’) isgreater than 10 for tetravalent metals (z=4), greater than 100 fordivalent and trivalent metals (z=2 or 3) and greater than 1400 for M=Al(z=3).

[0083] The zeolite catalysts preferably used in the process according tothe invention have, for M=Al, an SiO₂/M₂O₃ molar ratio of from greaterthan 1400 to 40,000:1, in particular from greater than 1400 to 5000:1,

[0084] for M=metal in oxidation state II or M=two or more metals inoxidation state II, have an SiO₂/MO molar ratio of from greater than 100to 40,000:1, in particular from greater than 200 to 5000:1,

[0085] for M=metal in oxidation state III or M=two or more metals inoxidation state III, have an SiO₂/M₂O₃ molar ratio of from greater than100 to 40,000:1, in particular from greater than 200 to 5000:1, and

[0086] for M=metal in oxidation state IV or M=two or more metals in 40oxidation state IV, have an SiO₂/MO₂ molar ratio of from greater than 10to 40,000:1, in particular from greater than 25 to 5000:1.

[0087] The zeolite catalyst used in the process according to theinvention is preferably of the pentasil type.

[0088] The upper limit of the modulus (40,000) is set only by the purityof the starting substances (residual traces of M or compounds of M) andthe purity and chemical resistance of the apparatuses employed in thesynthesis of the zeolite.

[0089] For a modulus below the stated limit, the Brönsted and Lewisacidity density (acidity density: acid centers/total catalyst surfacearea) of the zeolites increases significantly, the achievable TEDA yieldand selectivity and the catalyst service life drop significantly, andthe cost of purifying the TEDA increases significantly.

[0090] Surprisingly, it has been found that the drastic reduction in theacidity within the zeolite crystal in the process according to theinvention due to the incorporation of divalent and/or trivalent metalsin the form of metal oxides (M for z=2 or 3) in the lattice in thenormal case during the hydrothermal synthesis results in the advantagesaccording to the invention, for example a significant improvement in theselectivity with respect to TEDA. Zeolites containing tetravalent metalsin the form of metal oxides (M for z=4) in the zeolite lattice alsoachieve improved selectivity with respect to TEDA in accordance with theinvention.

[0091] For the zeolite catalyst, preferably of the pentasil type, havingmoduli as indicated above, there are neither additional requirementswith respect to the zeolite material as such nor with respect to theprocess by which this is obtainable.

[0092] In the zeolite catalyst used in the process according to theinvention, which, besides SiO₂, also contains one or more metals M inoxidation states II, III or IV as oxides, the metal M in oxidation stateII is preferably selected from the group consisting of Zn, Sn and Be,and mixtures thereof,

[0093] the metal M in oxidation state III is preferably selected fromthe group consisting of Al, B, Fe, Co, Ni, V, Mo, Mn, As, Sb, Bi, La,Ga, In, Y, Sc and Cr, and mixtures thereof, and

[0094] the metal M in oxidation state IV is preferably selected from thegroup consisting of Ti, Zr, Ge, Hf and Sn, and mixtures thereof.

[0095] Preference is given to zeolites in which M is aluminum, gallium,titanium, zirconium, germanium, iron or boron. Those in which M isaluminum, titanium, iron or boron are particularly preferred.

[0096] Examples of suitable zeolite catalysts of the pentasil type whichare to be employed in accordance with the invention are the followingtypes: ZSM-5 (as disclosed in U.S. Pat. No. 3,702,886), ZSM-11 (asdisclosed in U.S. Pat. No. 3,709,979), ZSM-23, ZSM-53, NU-87, ZSM-35,ZSM-48 and mixed structures comprising at least two of theabovementioned zeolites, in particular ZSM-5 and ZSM-11, and mixedstructures thereof.

[0097] Particular preference is given for the process according to theinvention to zeolites having an MFI or MEL structure or an MEL/MFI orMFI/MEL mixed structure.

[0098] The zeolites used in according with the invention are crystallinemetal silicates having an ordered channel and cage structure withmicropores. The network of such zeolites is built up from SiO₄ andM_(2/z)O (z=2, 3 or 4) tetrahedra which are bonded via joint oxygenbridges. A review of the known structures is given, for example, in W.M. Meier, D. H. Olsen and Ch. Baerlocher in “Atlas of Zeolite StructureTypes”, Elsevier, 4^(th) Edition, London 1996.

[0099] Also suitable in accordance with the invention are zeolites whichcontain no aluminum (M=Al) and in which the Si(IV) in the zeolitelattice has been partially replaced by a metal M(IV), for example Ti,Zr, Ge, Hf and/or Sn, partially by a metal M(II), for example Zn, Snand/or Be, and/or partially by a metal M(III), for example B, Fe, Co,Ni, V, Mo, Mn, As, Sb, Bi, La, Ga, In, Y, Sc and/or Cr

[0100] (II=oxidation state 2, III=oxidation state 3, IV=oxidation state4).

[0101] Said zeolites are usually prepared by reacting a mixture of anSiO₂ source and a metal source (for example M=Al, Zn, Be, B, Fe, Co, Ni,V, Mo, Mn, As, Sb, Bi, La, Ga, In, Y, Sc, Cr, Ti, Zr, Ge, Hf and/or Snin the oxidation states as described above) and a nitrogen-containingbase as template (“template compound”), for example tetraalkylammoniumsalt, if desired with addition of basic compounds (for example causticlyes), in a pressure vessel under elevated temperature for a period ofseveral hours or a few days, giving a crystalline product. This isseparated of (for example filtered off, spray-dried or precipitated),washed, dried and, for removal of the organic nitrogen base, calcined atelevated temperature (see below). The synthesis is optionally alsopossible without a template if the formation of the zeolite isguaranteed. In the resultant powder, the metal (for example M=Al, Zn,Be, B, Fe, Co, Ni, V, Mo, Mn, As, Sb, Bi, La, Ga, In, Y, Sc, Cr, Ti, Zr,Ge, Hf and/or Sn in the oxidation states as described above) is at leastpartly present within the zeolite lattice in varying proportions withtetra-, penta- or hexa-coordination.

[0102] The zeolites used in according with the invention can be preparedby the process described and/or are commercially available.

[0103] If the zeolite catalyst to be employed in according with theinvention, preferably of the pentasil type, is not at least partly inthe preferred acidic H⁺ form and/or NH₄ ⁺ form owing to the type ofproduction, but is, for example, in the Na⁺ form (or any othermetal-salt form desired), this can, in according with the prior art, beconverted at least partly into the preferred H⁺ and/or NH₄ ⁺ form by ionexchange, for example with ammonium ions, followed by calcination (seebelow). The treatment with dilute protic acid, for example mineral acid,which is likewise known from the literature for conversion of thezeolite at least partly into the H⁺ form is just as practicable.Suitable here are all protic acids, for example hydrochloric acid orsulfuric acid (see below).

[0104] It is subsequently possible to convert the zeolite catalystexchanged in this way into the desired Me⁺ form and contains H⁺ and/orNH₄ ⁺ by ion exchange with a corresponding metal-salt solution (metalMe=alkali metal, alkaline-earth metal or transition metal).

[0105] In order to achieve the highest possible selectivity, highconversions and particularly long catalyst service lives, it may beadvantageous to modify the zeolite catalysts as claimed.

[0106] A suitable modification of the zeolite catalysts consists in, asdescribed in ‘J. Weitkamp et al., Catalysis and Zeolites, Chapter 3:Modification of Zeolites, Springer Verlag, 1999’, subjecting the zeolitematerial—shaped or unshaped—to treatment in accordance with the knownprior art (EP-A-382 055, p. 4, lines 2ff+lines 20ff; DE-C2-24 34 913, p.3, lines 23ff; U.S. Pat. No. 5,041,548, p. 4, lines 27ff) withconcentrated or dilute protic acids—for example hydrochloric acid,sulfuric acid, hydrofluoric acid, phosphoric acid, a carboxylic acid,dicarboxylic acid or polycarboxylic acid—and/or complexing agents—forexample acetylacetonate (acac), nitrilotriacetic acid, sulfosalicylicacid, ethylenediaminetetraacetic acid (EDTA)—for example in accordancewith EP-A-842 936 and RU-C1-21 14 849, and/or steam.

[0107] In a particular embodiment, doping of the zeolites used in theprocess according to the invention can be carried out by application oftransition metals, sub-groups I to VIII, preferably from sub-groups I,II, IV and VIII, particularly preferably Zn, Ti, Zr, Fe, Co, Ni, Cr orV.

[0108] The application can be carried out by impregnation of the zeoliteused in the process according to the invention in aqueous metal-saltsolutions, by spraying corresponding metal-salt solutions onto thezeolite or by other suitable methods known from the prior art. Suitablemetal salts for the preparation of the metal-salt solutions are thenitrates, nitrosylnitrates, halides, carbonates, carboxylates,acetylacetonates, chloro complexes, nitro complexes or amine complexesof the corresponding metals, the nitrates and nitrosyl nitrates beingpreferred. In the case of zeolites which have been doped with aplurality of metals, the metal salts or metal-salt solutions can beapplied simultaneously or successively.

[0109] The zeolites coated or impregnated with the metal-salt solutionsare subsequently dried, preferably at temperatures of from 60 to 150°C., and optionally calcined at temperatures of from 200 to 950° C.,preferably from 400 to 750° C. In the case of separate impregnation, thecatalyst is dried after each impregnation step and optionally calcinedas described above. The sequence in which the transition metals areimpregnated is freely selectable. The coated and dried and optionallycalcined zeolites are subsequently optionally activated by treatment ina gas stream containing free hydrogen at temperatures of from 30 toapproximately 600° C., preferably from 150 to approximately 450° C. Thegas stream preferably consists of from 50 to 100% by volume of hydrogenand from 0 to 50% by volume of nitrogen.

[0110] The transition-metal solutions are applied to the zeolite in suchan amount that the total content of transition metal, in each case basedon the total weight of the catalyst, is from approximately 0.01 toapproximately 10% by weight, preferably from approximately 0.01 to 5% byweight, further preferably from approximately 0.01 to approximately 2%by weight and in particular from approximately 0.05 to 1% by weight.

[0111] The transition-metal surface area on the catalyst is in totalpreferably from approximately 0.01 to approximately 10 m²/g, furtherpreferably from 0.05 to 5 m²/g and in particular from approximately 0.05to 3 m²/g (M² per g of the catalyst). The metal surface area isdetermined by the chemisorption method described by J. LeMaitre et al.In “Characterization of Heterogeneous Catalysts”, Editor FrancisDelanny, Marcel Dekker, New York 1984, pp. 310-324.

[0112] In order to increase the service life, the zeolites to beemployed in accordance with the invention may be supported, for exampleon cellulose materials, clays, polymers, metals, graphites, binders ormetal oxides, such as aluminas, aluminum oxide or silicon dioxide. It isfurthermore possible to employ this as granules, in bead form or appliedto glass or other elements, for example woven fabrics (in particularmetal meshes) of any type.

[0113] Solidifying shaping processes which can be employed for thezeolites to be employed in accordance with the invention are inprinciple all methods for achieving corresponding shaping. Preference isgiven to processes in which the shaping is carried out by tableting orextrusion. Particular preference is given to processes in which theshaping is carried out by extrusion in conventional extruders, forexample to give extrudates having a diameter of usually from 1 to 10 mm,in particular from 2 to 5 mm. If binders and/or auxiliaries arerequired, the extrusion or tableting is advantageously preceded by amixing or compounding process. If desired, the extrusion/tableting isalso followed by a calcination step. The moldings obtained are, ifdesired, comminuted, preferably to give granules or grit having aparticular diameter of from 0.5 to 5 mm, in particular from 0.5 to 2 mm.These granules or grit and also catalyst moldings generated in anothermanner contain virtually no relatively fine-grained components thanthose having a minimum particle diameter of 0.5 mm.

[0114] In a preferred embodiment, the shaped zeolite to be employed inaccording with the invention comprises up to 80% by weight of binders,based on the total weight of the catalyst. Particularly preferred bindercontents are from 1 to 60% by weight, in particular from 20 to 45% byweight. Suitable binders are in principle all compounds employed forpurposes of this type, preferably compounds, in particular oxides, ofsilicon, aluminum, boron, phosphorus, zirconium and/or titanium. ofparticular interest as binder is silicon dioxide, where the SiO₂ mayalso be introduced into the shaping process as silica sol or in the formof tetraalkoxysilanes. Also suitable as binders are oxides of magnesiumand beryllium and clays, for example montmorillonite, kaolins,bentonites, halloysites, dickites, nacrites and anauxites.

[0115] Examples of auxiliaries which may be mentioned for thesolidifying shaping processes are extrusion auxiliaries; a conventionalextrusion agent is methylcellulose. Agents of this type are generallyburnt completely in the subsequent calcination step.

[0116] The calcination of the zeolite catalyst to be employed inaccording with the invention is carried out at temperatures of from 250to 950° C., preferably at from 400 to 750° C., particularly preferablyat from 450 to 600° C., for the duration of, in general, at least onehour, preferably for 2-5 hours. The calcination is carried out in a gasatmosphere, for example nitrogen, air or noble-gas atmosphere. Ingeneral, the calcination is carried out in oxygen-containingatmospheres, with the oxygen content being from 0.1 to 90% by volume,preferably from 0.2 to 22% by volume, particularly preferably from 10 to22% by volume. The use of other oxygen-supplying substances is likewisepossible. The long-term “oxygen-supplying substances” covers allsubstances which are capable of releasing oxygen under the statedcalcination conditions. Particular mention may be made of nitrogenoxides of the formula N_(x)O_(y), where x and y are selected so as togive a neutral nitrogen oxide, N₂O, an N₂O-containing offgas stream froman adipic acid plant, NO, NO₂, ozone or a mixture of two or morethereof. On use of CO₂ as oxygen-supplying substance, temperatures offrom 500° C. to 800° C. are preferably set during the calcination.Calcination under a steam atmosphere is likewise possible.

[0117] It has furthermore been recognized in accordance with theinvention that, after use of the zeolite catalyst used in accordancewith the invention, this can be regenerated, irrespective of its form,for example after a decrease in the activity and/or selectivity, by amethod in which the regeneration is carried out by targeted burning-offof the coatings responsible for the deactivation. This is preferablycarried out in an inert-gas atmosphere containing precisely definedamounts of oxygen-supplying substances. A regeneration method of thistype is described, inter alia, in WO 98/55228 and DE-Al-19 72 39 49, thedisclosure content of which is expressly incorporated herein in its fullscope by way of reference.

[0118] After the regeneration, the activity and/or selectivity of thecatalyst is increased compared with the state immediately before theregeneration.

[0119] The zeolite catalyst to be employed in accordance with theinvention and regenerated is heated to a temperature in the range fromapproximately 250° C. to 800° C., preferably from approximately 400° C.to 550° C. and in particular from approximately 450° C. to 500° C.,either in the reaction apparatus (reactor) or in an external oven in anatmosphere containing from 0.1 to approximately 20 parts by volume ofoxygen-supplying substances, particular preferably from 0.1 toapproximately 20 parts by volume of oxygen. The heating is preferablycarried out at a heating rate of from approximately 0.1° C./min. toapproximately 20° C./min., preferably from approximately 0.3° C./min. toapproximately 15° C./min. and in particular from 0.5° C./min. to 10°C./min.

[0120] During this heating phase, the catalyst is heated to atemperature at which the mostly organic coatings located thereon beginto decompose, while at the same time the temperature is regulated viathe oxygen content and thus does not increase in such a way that damageto the catalyst structure occurs. The slow increase in the temperatureor the holding at low temperature through adjustment of thecorresponding oxygen content and the corresponding heating power is anessential step toward preventing local overheating of the catalyst inthe case of high organic contents of the catalyst to be regenerated.

[0121] If the temperature of the offgas stream at the reactor outletdrops in spite of the increasing amounts of oxygen-supplying substancesin the gas stream, the burning-off of the organic coatings isterminated. The duration of the treatment is generally in each case fromapproximately 1 to 30 hours, preferably from approximately 2 toapproximately 20 hours and in particular from approximately 3 toapproximately 10 hours.

[0122] During subsequent cooling of the catalyst regenerated in thisway, it must be ensured that the cooling does not take place too quickly(“quenching”) since otherwise the mechanical strength of the catalystmay be adversely affected.

[0123] It may be necessary to subject the catalyst, after theregeneration carried out by calcination, as described above, to rinsingwith water and/or dilute acids, for example hydrochloric acid, in order,where necessary, to remove the inorganic content of the catalyst (alkalimetal traces, etc.) remaining due to the contamination of the startingmaterials. Re-drying and/or calcination of the catalyst can subsequentlybe carried out.

[0124] In a further embodiment of the process according to theinvention, the at least partially deactivated catalyst is, before theheating in accordance with the regeneration procedure, washed with asolvent in the reaction reactor or in an external reactor in order toremove target product still adhering. The washing here is carried out insuch a way that, although the target products adhering in each case tothe catalyst can be removed therefrom, the temperature and pressure are,however, not selected to be so high that the mostly organic coatings arelikewise removed. The catalyst here is preferably merely rinsed with asuitable solvent. Suitable for this washing operation are thus allsolvents in which the respective reaction product is readily soluble.The amount of solvent used and the duration of the washing operation arenot crucial. The washing operation can be repeated a number of times andcan be carried out at elevated temperature. On use of CO₂ as solvent,supercritical pressure is preferred, otherwise the washing operation canbe carried out under atmospheric pressure or superatmospheric pressureor sub-critical pressure. When the washing operation is complete, thecatalyst is generally dried. Although the drying operation is generallynot crucial, the drying temperature should not greatly exceed theboiling point of the solvent used for the washing in order to avoidsudden evaporation of the solvent into the pores, in particular into themicropores, since this too may result in damage to the catalyst.

[0125] A preferred embodiment of the preparation process may consist inthat the continuous process according to the invention for the synthesisof TEDA need not be interrupted during regeneration of the catalystaccording to the invention in order to increase the process throughput.This can be achieved by the use of at least two reactors connected inparallel, which can be operated alternately.

[0126] The catalyst regeneration can be carried out in such a way thatat least one of the reactors connected in parallel is decoupled from therespective reaction step, and the catalyst present in this reactor isregenerated, where at least one reactor is always available for thereaction of EDA in each step during the continuous process.

[0127] The TEDA obtained in accordance with the invention can berecrystallized from suitable solvents (for example pentane or hexane) inorder to improve its purity. However, this is usually unnecessary sinceTEDA can be prepared by the process according to the invention withpurities of greater than 95% by weight, for example greater than 97% byweight.

[0128] In a particular embodiment, the TEDA preparation process asclaimed is combined with the subsequent TEDA process according to theearlier EP application No 00114475.7 of Jul. 6, 2000 (BASF AG).

[0129] In accordance with this combination, firstly TEDA is prepared asclaimed. In the subsequent work-up of the TEDA (for example bydistillation), which may be multistep, the TEDA is evaporated,preferably in the final work-up step (in particular distillation orrectification step), and the vapor-form TEDA obtained, for example, atthe top or in a side take-off of the distillation column, whichpreferably has a purity of greater than 95% by weight, in particulargreater than 97% by weight, is introduced into a liquid solvent. Thisintroduction of the vapor-form TEDA directly into a liquid solvent isalso referred to below as TEDA quenching.

[0130] By subsequent crystallization of the TEDA out of the resultantsolution, pure TEDA of high quality is obtained.

[0131] The liquid solvent is generally selected from the groupconsisting of cyclic or acyclic hydrocarbons, chlorinated aliphatichydrocarbons, aromatic hydrocarbons, alcohols, ketones, aliphaticcarboxylic esters, aliphatic nitrites and ethers.

[0132] For the preparation of a solution of pure TEDA in accordance withthe above process combination which can be used, for example, ascatalyst solution in the production of polyurethane foam, the solventemployed for the TEDA quenching is preferably an alcohol (for exampleethylene glycol, 1,4-butanediol or preferably dipropylene glycol). Thecolor number of a 33% strength by weight TEDA solution in dipropyleneglycol obtained in this way is less than 150 APHA, in particular lessthan 100 APHA, very particularly less than 50 APHA.

[0133] For the preparation of pure (crystalline) TEDA in accordance withthe above process combination, the solvent used for the TEDA quenchingis preferably an aliphatic hydrocarbon, in particular a saturatedaliphatic hydrocarbon having 5 to 8 carbon atoms (for example hexane,heptane or preferably pentane). The crystallization of the pure TEDAfrom the TEDA solution prepared in accordance with the invention can becarried out by methods known to the person skilled in the art. The TEDAcrystals obtained by subsequent multistep, or preferably single-step,crystallization are of high purity (purity of, in general, at least99.5% by weight, in particular at least 99.8% by weight, content of PIPless than 0.1% by weight, in particular less than 0.05% by weight,content of N-ethylpiperazine less than 0.02% by weight, in particularless than 0.01% by weight), and the color number of a 33% strength byweight solution in dipropylene glycol is less than 50 APHA, inparticular less than 30 APHA.

[0134] (All APHA numbers in accordance with ISO 6271).

[0135] The introduction of the vapor-form TEDA into the liquid solventis carried out in a quenching apparatus, for example preferably in afalling-film condenser (thin-film, trickle-film or falling-flowcondenser) or in a jet apparatus. The vapor-form TEDA here can betransported in cocurrent or in countercurrent with the liquid solvent.It is advantageous to introduce the vapor-form TEDA into the quenchingapparatus from the top. It is furthermore advantageous to feed theliquid solvent in tangentially at the top of the falling-film condenseror to feed the liquid solvent through one or more nozzles in order toachieve complete wetting of the interior wall of the quenchingapparatus.

[0136] In general, the temperature in the TEDA quenching is set bycontrolling the temperature of the solvent employed and/or of thequenching apparatus to from 20 to 100° C., preferably from 30 to 60° C.The absolute pressure in the TEDA quenching is generally from 0.5 to 1.5bar.

[0137] In general, depending on the type of solvent, firstly solutionshaving a TEDA content of from about 1 to 50% by weight, preferably from20 to 40% by weight, are obtained during the TEDA quenching.

EXAMPLES

[0138] Catalyst A:

[0139] Firstly, a TS-1 zeolite powder (pentasil, MFI structure) wasprepared as described in Example 1 of DE-A-196 23 611 (SiO₂/TiO₂=40[mol/mol]). Before the extrusion with 20% by weight of SiO₂ (based onthe total weight of the finished extrudates), the zeolite powder wastreated with 5 M HCl, washed a number of times with water and calcinedat 500° C. for 5 hours. The 2 mm extrudates were subsequently calcinedat 500° C. for 5 hours.

Example 1

[0140] Continuous Preparation of TEDA

[0141] The catalyst shown in the table below was employed in a gas-phaseapparatus (heated tubular reactor: length: 1000 mm, diameter 6 mm).Starting-material mixture: 35% of EDA, 15% of PIP, 50.0% of water (alldata in % by weight). The aqueous starting-material mixture was pumpeddirectly into the reactor and evaporated in the upper part at a reactiontemperature of 345° C. before being passed onto the catalyst withoutpressure. Weight hourly space velocity: 1.0 kg of starting-materialmixture/kg of catalyst*h. The reaction products were condensed at thereactor outlet in a condenser and collected, and an aliquot was analyzedby gas chromatography.

[0142] GC Analysis:

[0143] Column: RTX-5, 30 m; temperature program: 80° C.-5° C./min.-280°C., detector: FID, internal standard: N-methylpyrrolidone (NMP).

[0144] Evaluation: TABLE 1 Synthesis of triethylenediamine (TEDA) fromethylenediamine (EDA) and piperazine (PIP); feed: 35:15:50 EDA:PIP:H₂Oin % by weight; modulus: SiO₂/TiO₂ molar ratio of the zeolites used.Modulus U_(EDA) U_(pip) S_(TEDA) Example Catalyst [SiO₂/M_(x)O_(x+1])[%] [%] [%] 1 A 40 >95 11 95 (M = Ti, x = 1)

[0145] (U=conversion in % by weight based on the employed amount ofsubstance given in the table (EDA or PIP);

[0146] S=Selectivity, based on reacted —CH₂—CH₂— units originating fromEDA and PIP).

We claim:
 1. A process for the preparation of triethylenediamine (TEDA)by reaction of ethylenediamine (EDA) in the presence of a zeolitecatalyst, wherein the zeolite catalyst comprises one or more metals M inoxidation states II, III or IV as oxides, and for M=Al, has an SiO₂/M₂O₃molar ratio of greater than 1400:1, for M=metal in oxidation state II orM=two or more metals in oxidation state II, has an SiO₂/MO molar ratioof greater than 100:1, for M=metal in oxidation state III or M=two ormore metals in oxidation state III, has an SiO₂/M₂O₃ molar ratio ofgreater than 100:1, and for M=metal in oxidation state IV or M=two ormore metals in oxidation state IV, has an SiO₂/MO₂ molar ratio ofgreater than 10:1, and the reaction temperature is from 250 to 500° C.2. A process as claimed in claim 1, wherein the reaction is carried outcontinuously.
 3. A process as claimed in claim 1 or 2, wherein thereaction is carried out in the gas phase.
 4. A process as claimed in oneof the preceding claims, wherein the reaction is carried out in thepresence of a solvent or diluent.
 5. A process as claimed in one of thepreceding claims, wherein the reaction is carried out in the presence ofwater and/or ammonia.
 6. A process as claimed in one of the precedingclaims, wherein the reaction is carried out in the presence of from 2 to1200% by weight of water, based on EDA employed.
 7. A process as claimedin one of the preceding claims, wherein the reaction is carried out inthe presence of from 14 to 300% by weight of water, based on EDAemployed.
 8. A process as claimed in one of the preceding claims,wherein EDA and one or more of the amine compounds from the groupconsisting of monoethanolamine, diethanolamine, triethanolamine,piperazine (PIP), diethylenetriamine, triethylenetetramine,tri(2-aminoethyl)amine, N-(2-aminoethyl)ethanolamine,N-(2-hydroxyethyl)piperazine and N-(2-aminoethyl)piperazine are reacted.9. A process as claimed in one of the preceding claims, wherein EDA andfrom 1 to 1000% by weight of piperazine (PIP), based on EDA, arereacted.
 10. A process as claimed in one of claims 1 to 8, wherein EDAand from 7 to 250% by weight of piperazine (PIP), based on EDA, arereacted.
 11. A process as claimed in one of claims 1 to 8, wherein EDA,from 8 to 250% by weight of PIP and from 23 to 300% by weight of water,in each case based on EDA, are reacted.
 12. A process as claimed in oneof the preceding claims, wherein PIP arising after the reaction isseparated off and fed back into the reaction with EDA.
 13. A process asclaimed in one of the preceding claims, wherein the consumption of PIPin the overall balance is from 0 to 30 kg per 100 kg of TEDA.
 14. Aprocess as claimed in one of the preceding claims, wherein the reactiontemperature is from 310 to 390° C.
 15. A process as claimed in one ofthe preceding claims, wherein the absolute pressure is from 0.1 to 10bar.
 16. A process as claimed in one of the preceding claims, whereinthe WHSV (weight hourly space velocity), based on the amines employed inthe reaction, is from 0.05 to 6 h⁻¹.
 17. A process as claimed in one ofthe preceding claims, wherein the zeolite catalyst, for M=Al, has anSiO₂/M₂O₃ molar ratio of from greater than 1400 to 40,000:1.
 18. Aprocess as claimed in one of the preceding claims, wherein the zeolitecatalyst, for M=metal in oxidation state II or M=two or more metals inoxidation state II, has an SiO₂/MO molar ratio of from greater than 100to 40,000:1.
 19. A process as claimed in one of the preceding claims,wherein the zeolite catalyst, for M=metal in oxidation state III orM=two or more metals in oxidation state III, has an SiO₂/M₂O₃ molarratio of from greater than 100 to 40,000:1.
 20. A process as claimed inone of the preceding claims, wherein the zeolite catalyst, for M=metalin oxidation state IV or M=two or more metals in oxidation state IV, hasan SiO₂/MO₂ molar ratio of from greater than 10 to 40,000:1.
 21. Aprocess as claimed in one of the preceding claims, wherein the zeolitecatalyst is of the pentasil type.
 22. A process as claimed in one of thepreceding claims, wherein the metal M in oxidation state II is selectedfrom the group consisting of Zn, Sn and Be, and mixtures thereof.
 23. Aprocess as claimed in one of the preceding claims, wherein the metal Min oxidation state III is selected from the group consisting of Al, B,Fe, Co, Ni, V, Mo, Mn, As, Sb, Bi, La, Ga, In, Y, Sc and Cr, andmixtures thereof.
 24. A process as claimed in one of the precedingclaims, wherein the metal M in oxidation state IV is selected from thegroup consisting of Ti, Zr, Ge, Hf and Sn, and mixtures thereof.
 25. Aprocess as claimed in one of the preceding claims, wherein the zeolitecatalyst is of the MFI or MEL structural type or mixed structuresthereof (MEL/MFI or MFI/MEL).
 26. A process as claimed in one of thepreceding claims, wherein the zeolite catalyst exists or is employed atleast partly in the H⁺ and/or NH₄ ⁺ form under the reaction conditionsif Al and/or other metals M are in oxidation state II or III in thezeolite.
 27. A process as claimed in one of the preceding claims,wherein the zeolite catalyst is treated with a protic acid before use inthe process.
 28. A process as claimed in one of the preceding claims,wherein the zeolite catalyst has been doped with one or more transitionmetals.
 29. A process as claimed in one of the preceding claims, whereinthe zeolite catalyst comprises silicon dioxide as binder.
 30. A processas claimed in one of the preceding claims, wherein a zeolite catalystwhich has been treated or regenerated in a gas atmosphere in thepresence of oxygen or oxygen-supplying substances at a temperature inthe range from 250 to 800° C. is employed at least partly.
 31. A processas claimed in one of the preceding claims, wherein the process iscarried out without interruption in at least two reactors connected inparallel, of which in each case one can be decoupled from thestarting-material and product stream for regeneration of the zeolitecatalyst.
 32. A process for the preparation of a solution of TEDA, whichcomprises preparing TEDA as claimed in one of the preceding claims,evaporating the prepared TEDA, and passing the vapor-form TEDA into aliquid solvent.
 33. A process for the preparation of TEDA, whichcomprises preparing a solution of pure TEDA as claimed in the precedingclaim, and subsequently crystallizing the TEDA out of this solution. 34.A process as claimed in one of the two preceding claims, wherein theliquid solvent is selected from the group consisting of cyclic oracyclic hydrocarbons, chlorinated aliphatic hydrocarbons, aromatichydrocarbons, alcohols, ketones, aliphatic carboxylic esters, aliphaticnitrites and ethers.